As an alternative to the viscose process, in recent years there has been described a number of processes wherein cellulose, without forming a derivative, is dissolved in an organic solvent, a combination of an organic solvent and an inorganic salt, or in aqueous saline solutions. Cellulose fibres made from such solutions have received by BISFA (The International Bureau for the Standardisation of man made Fibres) the generic name Lyocell. As Lyocell, BISFA defines a cellulose fibre obtained by a spinning process from an organic solvent. By "organic solvent", BISFA understands a mixture of an organic chemical and water. "Solvent-spinning" means dissolving and spinning without derivatisation.
So far, however, only one process for the production of a cellulose fibre of the Lyocell type has achieved industrial-scale realization. In this process, a tertiary amine-oxide, particularly N-methylmorpholine-N-oxide (NMMO) is used as a solvent. Such a process is described e.g. in U.S. Pat. No. 4,246,221 and provides fibres having a high tensile strength, a high wet-modulus and a high loop strength.
However, the usefulness of plane assemblies such as fabrics produced from the above fibres is significantly restricted by the pronounced tendency of these fibres to fibrillate when wet. Fibrillation means breaking off of the wet fibre in longitudinal direction at mechanical stress, so that the fibre gets hairy, furry. A fabric made from these fibres and dyed significantly loses colour intensity as it is washed several times. Additionally, light stripes are formed at abrasion and crease edges. The reason for fibrillation may be that the fibres consist of fibrils arranged in fibre direction and that there is only little crosslinking between these.
Moreover, stripes may also form when rope-shaped fibre assemblies are dyed. In plane textile assemblies, small knots may form through friction in dry condition, a property known as "pilling".
WO 92/07124 describes a process for the production of a fibre having a reduced tendency to fibrillation, according to which the freshly spun, i.e. not yet dried fibre is treated with a cationic polymer. As such a polymer, a polymer having imidazole and azetidine groups is indicated. Additionally, a treatment with an emulsifiable polymer, such as polyethylene or polyvinylacetate, or a crosslinking with glyoxal may be carried out.
In a lecture held by S. Mortimer at the CELLUCON conference 1993 in Lund, Sweden, it was mentioned that the tendency to fibrillation rises as drawing is increased.
EP-A-0 538 977 and WO 94/09191 describe a process of the type initially mentioned, wherein fibres of the Lyocell type are contacted with a textile auxiliary agent to reduce their tendency to fibrillation.
WO 94/24343 describes a process for the production of cellulose fibres having a reduced tendency to fibrillation, in which process a solution of cellulose in a tertiary amine-oxide is spun into fibres and the freshly spun fibres are contacted with a textile auxiliary agent carrying at least two reactive groups and are washed with an aqueous buffer, not using glyoxal as a textile auxiliary agent. According to this known process, the freshly spun fibres are best contacted with the textile auxiliary agent in an alkaline medium.
It is further known that fibre assemblies made from fibres of the Lyocell type can be crosslinked with methylol compounds to produce wash-resistant wovens and knit fabric. It has been shown however that when these compounds are used it is not possible to prevent the formation of abrasion edges during dyeing. To prevent these, crosslinking would have to be carried out before dyeing or at latest during dyeing. However, methylol compounds as well as the other conventional high-grade finishing agents are hardly appropriate for that purpose. Another drawback of the methylol compounds is the formation of formaldehyde, implying pollution at the workplace.